Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit battery) of the middle- or large-sized battery module. Especially, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
FIG. 1 is a perspective view typically illustrating a conventional representative pouch-shaped battery. A pouch-shaped battery 10 shown in FIG. 1 is configured in a structure in which two electrode terminals 11 and 12 protrude from the upper and lower ends of a battery body 13, respectively, while the electrode terminals 11 and 12 are opposite to each other. A sheathing member 14 includes upper and lower sheathing parts. That is, the sheathing member 14 is a two-unit member. An electrode assembly (not shown) is received in a receiving part which is defined between the upper and lower sheathing parts of the sheathing member 14. The opposite sides 14b and the upper and lower ends 14a and 14c, which are contact regions of the upper and lower sheathing parts of the sheathing member 14, are bonded to each other, whereby the pouch-shaped battery 10 is manufactured. The sheathing member 14 is configured in a laminate structure of a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 14b and the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 14b and the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14 so as to weld the resin layers thereof to each other. According to circumstances, the opposite sides 14b and the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14 may be bonded to each other using a bonding agent. For the opposite sides 14b of the sheathing member 14, the same resin layers of the upper and lower sheathing parts of the sheathing member 14 are in direct contact with each other, whereby uniform sealing at the opposite sides 14b of the sheathing member 14 is accomplished by welding. For the upper and lower ends 14a and 14c of the sheathing member 14, on the other hand, the electrode terminals 11 and 12 protrude from the upper and lower ends 14a and 14c of the sheathing member 14, respectively. For this reason, the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14 are thermally welded to each other, while a film-shaped sealing member 16 is interposed between the electrode terminals 11 and 12 and the sheathing member 14, in consideration of the thickness of the electrode terminals 11 and 12 and the difference in material between the electrode terminals 11 and 12 and the sheathing member 14, so as to increase sealability of the sheathing member 14.
However, the mechanical strength of the sheathing member 14 is low, and therefore, a plurality of battery cells (unit batteries) are mounted in a pack case, such as a cartridge, so as to manufacture a battery module having a stable structure. In this case, however, a device or a vehicle, in which a middle- or large-sized battery module is installed, has a limited installation space. Consequently, when the size of the battery module is increased due to the use of the pack case, such as the cartridge, space utilization is lowered. Also, due to their low mechanical strength, the battery cells repeatedly expand and contract during the charge and discharge of the battery cells, with the result that the thermally welded regions of the sheathing member may be easily separated from each other.
Meanwhile, battery cells constituting such a middle- or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. In particular, the laminate sheet of each pouch-shaped battery widely used in the battery module has a polymer material exhibiting low thermal conductivity coated on the surface thereof, with the result that it is difficult to effectively lower the overall temperature of the battery cells.
If the heat, generated from the battery module during the charge and discharge of the battery module, is not effectively removed, the heat accumulates in the battery module, with the result that the deterioration of the battery module is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
Each battery module mounted in a middle- or large-sized battery module is generally manufactured by stacking a plurality of battery cells with high integration. Electrode terminals of neighboring battery cells are electrically connected to each other.
FIG. 2 is a perspective view typically illustrating the electrical connection structure of a conventional representative battery module.
Referring to FIG. 2, a battery module 50 is configured in a structure in which a plurality of battery cell units 20 are connected in series to one another in a stacked manner, and two battery cells 10 are connected in series to each other in each of the battery cell units 20.
In the battery module 50, therefore, electrode terminals 11 and 12 of the battery module 40 are located at the same side irrespective of the number of the battery cell units 20, with the result that the battery module 50 is arranged in a restricted form.
Also, in a case in which the batteries are cooled in an air cooling manner, a flow space is formed in consideration of the structure of the battery module. For a battery module in which electrode terminals are located at the same side as described above, however, a cooling structure is also restricted.
Meanwhile, as demand for vehicle systems, such as electric vehicles and plug-in hybrid electric vehicles, requiring a high-capacity battery pack has increased, demand for high-power, large-capacity battery modules has also increased. On the other hand, the total capacity of the battery module 50 having the structure as shown in FIG. 2 is substantially decided based on each of the battery cells 10 constituting the battery cell units 20, with the result that manufacturing a desired large-capacity battery pack is limited.
Consequently, there is a high necessity for a battery module that provides high power and large-capacity and that can be flexibly configured based on a limited space and cooling structure.